[BUG] sessions-index.json stops being updated after v2.1.31 — new sessions invisible to /resume

Bug Description

After updating to Claude Code v2.1.31, new sessions are no longer being registered in sessions-index.json. Session .jsonl files are still being written to disk, but the index that /resume reads from stopped being updated. This makes all sessions created after the update invisible to /resume.

Reproduction Steps

1. Update to Claude Code v2.1.31+ (confirmed on 2.1.31 through 2.1.34)
2. Start a new session, do some work, exit
3. Run claude and use /resume to find the session
4. Session does not appear in the list

Diagnosis

# Count .jsonl session files vs indexed entries
PROJ_DIR=~/.claude/projects/<your-project-dir>
echo "JSONL files on disk: $(ls $PROJ_DIR/*.jsonl 2>/dev/null | wc -l)"
echo "Entries in index:    $(python3 -c "import json; print(len(json.load(open('$PROJ_DIR/sessions-index.json'))['entries']))")"
echo "Index last modified: $(stat -f '%Sm' -t '%Y-%m-%d %H:%M' $PROJ_DIR/sessions-index.json)"

In my case:

• 98 .jsonl files on disk
• 37 entries in sessions-index.json
• 6 real sessions created after Feb 4 are not indexed (the rest of the gap is agent sub-sessions, file-history snapshots, etc. that were never meant to be indexed)
• Index was last modified 2026-02-04 09:09 — the day v2.1.31 was installed
• The newest indexed session is from 2026-02-03

Workaround

If you know the session ID (from the .jsonl filename), you can still resume directly:

claude --resume <session-id>

But browsing/searching via /resume won't show any session created after the index stopped updating.

Environment

• Claude Code versions: 2.1.31, 2.1.32, 2.1.33, 2.1.34 (all affected)
• Last working version: Unknown, but index has entries up to 2026-02-03 (likely 2.1.30 or earlier)
• Platform: macOS Darwin 25.2.0
• Node: v22.22.0

Related Issues

• #22030 — similar symptom (stale sessions-index.json) but different root cause (metadata drift vs index not being written at all)
• #14157 — similar pattern of /resume regression after version update
• #18311 — sessions exist on disk but not discoverable